Heat pump-type hot water supply devices that heat water by means of a refrigerant in a refrigeration cycle to produce hot water have widely been used. The heat pump water heaters each include a water-refrigerant heat exchanger that heats water to provide hot water by means of heat exchange between a high-temperature refrigerant and the water. Solids generally called scale adhere to the inner wall of a water flow path inside the water-refrigerant heat exchanger. The scale is mainly formed as a result of deposition of precipitated calcium solute in the water. As the water temperature is higher, the solubility of calcium is lower. Thus, in the case of water having a high calcium hardness, during the process of heating water in the water-refrigerant heat exchanger, calcium carbonate precipitates and scale is thereby generated. If the flow path is narrowed as a result of accumulation of the scale, the flow path resistance becomes large and the water flow rate is thus lowered, causing an adverse effect on the operation of the heat pump water heater.
Patent Literature 1 discloses a heat pump water heater including: water flow rate detecting means for detecting a water flow rate of a hot water supply circuit in order to detect an abnormality of a water circuit due to, e.g., accumulation of scale; and water circuit abnormality detecting means for driving a pump at a predetermined rotation speed, detecting the water flow rate via the water flow rate detecting means, and if the water flow rate is smaller than a water flow rate set in advance, determines that a water circuit abnormality occurs.